The present technology relates to a power semiconductor device and a method of manufacturing the same.
Generally, power semiconductor devices are widely used to control motors or as elements of various switching devices such as inverters, and the like.
In detail, the power semiconductor device, a semiconductor device used in a power apparatus, is the core component of the power apparatus optimized for converting or controlling power.
The power semiconductor device has a higher breakdown voltage, a higher current level, and a higher frequency as compared with a general semiconductor device.
As typical power semiconductor devices, there exist metal oxide semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), and the like.
IGBTs and MOSFETs basically have an npn junction structure. That is, two diodes are connected to each other so that rectifying directions thereof are opposed to each other, such that a current does not flow therein at an ordinary time.
However, in the case in which a positive (+) voltage is applied to a gate formed in a manner in which it is insulated from a p-type semiconductor region using an oxide, electrons in the p-type semiconductor region are drawn, such that a conductive channel is formed in a location where the p-type semiconductor region and the oxide abut each other.
A current flows between an emitter and a collector or between a source and a drain through the conductive channel.
A MOSFET is a device having only a flow of either an electron current or a hole current, unlike an IGBT.
Representative characteristics of such a MOSFET are forward voltage drop and breakdown voltage.
In a MOSFET, since a path through which a current of the device may flow is limited to a channel, current density of the device is low, such that the forward voltage drop is large.
Further, in order to increase the breakdown voltage of the power semiconductor device in a turned-off state, adrift layer of the power semiconductor device should be thick, and a concentration of impurities thereof should be low, which inevitably causes a forward voltage drop.
In order to improve both of the forward voltage drop and the breakdown voltage with a trade-off relationship therebetween, a MOSFET having a RESURF structure has been introduced.
A RESURF structure is a structure in which p-type semiconductor regions and n-type semiconductor regions are alternately formed in a direction of width of the device or a lateral direction by forming the p-type semiconductor regions in an n-type drift layer.
In such a MOSFET having the RESURF structure, characteristics such as a high epitaxial layer concentration, a high breakdown voltage and a low forward voltage drop in a thin drift layer due to a charge compensation effect may be obtained.
Generally, when a reverse voltage is applied to the power semiconductor device, a depletion region is extended due to the presence of an electric field.
As the reverse voltage is increased, the depletion region is also increased. Therefore, space sufficient to extend the depletion region should be provided in order to obtain a high breakdown voltage.
As described above, the n-type semiconductor regions and the p-type semiconductor regions are alternately formed in the RESURF structure.
Generally, the p-type semiconductor region and the n-type semiconductor region are formed in a longitudinal direction or direction of height of the power semiconductor device so as to have a width similar to each other. However, due to limitations in the manufacturing process, a lower p-type semiconductor region has a width larger than that of the n-type semiconductor region.
In this case, the space sufficient to extend the depletion region is not present when the applied reverse voltage is gradually increased, such that the breakdown voltage is decreased.
Therefore, there is needed a power semiconductor device having a forward voltage drop effect by having a RESURF structure, and having a breakdown voltage higher than that of a power semiconductor device having a RESURF structure according to the prior art.
The following Prior art document (Patent Document 1) relates to an insulated semiconductor device and a method of manufacturing the same. However, Patent Document 1 does not disclose a feature in which each of a width and a concentration of a second conductivity type pillar is changed in the longitudinal direction or the direction of height of the device.